What is a stop in photography?

Photography jargon can be a quick way for photographers to talk to each other. But if you don’t know the words it can be confusing. A “stop” is something that is talked about a lot in photography and is one of those shorthand terms it is very helpful to understand. So, what is a stop in photography?

A “stop” is a measurement for comparing amounts of light

Photographers use the term “stop” to compare the amount of light let into their camera and the amount of light seen in a final image. It can be applied to aperture, shutter speed and ISO because each of these controls how much light reaches the camera sensor to create an exposure. Sometimes, it is used when talking about a finished image to compare how bright or dark one part of an image is compared to another part. It may also be used to suggest by how much an image could be brightened or darkened to improve it.

A “stop” means either doubling or halving the amount of light

Whether you are changing the amount of light let in to your sensor by changing the aperture, shutter speed or ISO, a stop means either doubling or halving the amount of light that reaches your sensor. You can double the amount of light by having the shutter open twice as long. Or, you can halve the amount of light by having it open half as long. For example, in the diagram, you can see that changing from 1/100th second to 1/200th second is a difference of 1 stop. If we make that change, it will halve the light that reaches the sensor as the shutter is open for half the time. Similarly, if we went from 1/800th second to 1/100th second, we would increase the light 3 stops – doubling it 3 times.

You can also double the amount of light by opening the aperture up 1 stop. Or, you can halve the light by closing the aperture one stop.

This diagram illustrates the relationship between the various f numbers in terms of stops. The circles represent how wide open the aperture is. So, you can see that f/2.8 is a very wide aperture, f/5.6 is a medium aperture and f/16 is a very small aperture. The difference in light between f/2.8 and f/16 is 5 stops. In other words, you halve the light 5 times if you go from f/2.8 to f/16.

You can make adjustments on many cameras that are smaller than a full stop. Normally, this means you can adjust by 1/3 of a stop at a time. So, you may find that your camera offers other numbers in between those shown here. Different lenses also allow for different sizes of aperture. Some allow bigger ones (e.g. 50mm f/1.4) and others allow smaller ones (e.g. for macro work).

You can also use the ISO to go up or down a stop or more. Similarly to shutter speed, ISO works by doubling or halving the number to give you the difference of one stop. So, ISO 200 is one stop more than ISO 100. Changing from ISO 100 to ISO 3200 means doubling 6 times. So this is a 6 stop difference with the light being doubled 6 times. It works the same going back down as well. So, if you go from ISO 400 to ISO 100 you are reducing the light by 2 stops – halving the amount of light twice.

Filters

Various filters are available to help you to change the amount of light let in to your camera’s sensor. These can be full Neutral Density (ND) filters, which are tinted all over. Or, you can get gradual or partial ND filters that have a tint for some of the filter. An extreme filter such as a 10 stop filter reduces the amount of light by 10 stops – you halve the amount of light 10 times. In other words you get approximately 1000 times less light reaching the sensor! They are a popular choice for artistic long exposure landscape photography. Polarising filters also reduce the light as well as having other effects. A polariser will typically reduce your light by about 2-3 stops.

If you want to balance the light in a landscape photo, you can do this by using a graduated ND filter to darken the sky. Spot meter the sky and the land and calculate the number of stops difference between the two. This will tell you what type of filter you need (e.g. 2 stop or 3 stop).

Summary

• What is a stop in photography? – A “stop” is a measurement in photography
• A “stop” means either doubling or halving the amount of light
• This can be changed using aperture, shutter speed, ISO and filters

© Joe Lenton, March 2015